1. Field of the Invention
The present invention relates to an indicating instrument and an initializing device for transmitting a rotation output of a stepping motor to an indicating needle via a speed-reducing gear mechanism. More specifically, the invention relates to the indicating instrument and the initializing device in which a stopped position of the indicating needle at the time of turning on or off an electric source is not substantially different from that after an ordinary control is made.
The ordinary control means that the indicating needle is controlled to stop at the position of the graduation “zero” when the vehicle or the like is stopped (vehicle speed or the like=zero) during ordinary running or the like.
2. Related Art Statement
According to the indicating instrument using the stepping motor as the driving source of the indicating needle, a reference position of the indicating needle is set by turning the indicating needle toward a zero-reset position and stopping the indicating needle at the zero-resetting position with a stopper so that a zero-return correction may be performed (See JP-A 2000-50695).
When the indicating needle is moving or when a magnetic rotor of the stepping motor is being rotated, induction voltage is generated in a field coil. When the indicating needle is stopped at the zero-reset position and the rotation of the magnetic rotor is stopped, no indication voltage is produced in the field coils. Therefore, during the time period when the stepping motor is driven in the zero-resetting direction, the magnetizing coil is switched to a non-magnetized state, and it is judged that the indicating needle reached the zero-reset position when the induction voltage generated in the field coils became not more than a preset threshold value. Then, the zero-return correction operation is terminated. See JP-A 2001-314099 and JP-A 2002-250641.
In the conventional indicating instrument, the position where turning of the indicating needle is mechanically stopped with a stopper mechanism is taken as a reference position of the indicating needle, and this reference position is taken as a zero position of graduation. Feeding of AC zero-resetting signals (AC signals to driving the stepping motor in a reverse direction) is stopped at the position where the turning of the indicating needle is mechanically stopped (i.e., in a state that a member to be turned is pushed against the stopper), thereby terminating the zero-return correction operation. Accordingly, if a slight play of the gears occurs at the stop position, the position where the member to be driven should be inherently stopped may be stepped out by the play of the gears.
It may be considered that after an over zero-resetting operation is performed in which AC resetting signals are continuously fed by a preset electric angle, without stopping the AC zero-resetting signals, at the position where the turning of the indicating needle is mechanically stopped, the indicating needle is turned by a preset angle in a direction away from the position where the turning of the indicating needle is mechanically stopped. Since the indicating needle is turned by the preset angle in the direction away from the position where the turning of the indicating needle is mechanically stopped, the zero-return phenomenon due to the backlash of the gears or the like can be prevented.
However, the position where the indicating needle is stopped when the needle is turned by the preset angle in the direction away from the position where turning of the indicating needle is mechanically stopped differs from the stopped position of the indicating needle after the ordinary control (for example, vehicle speed=zero) owing to the backlash. More specifically, when the zero-return correction is effected, the stepping motor is rotated in a normal direction to turn the indicating needle to the position of the graduation “0”, for example. On the other hand, in the ordinary control, the stepping motor is rotated in the reverse direction to return the indicating needle to the position of the graduation “0”. Consequently, the stopped position of the indicating needle after the zero-return correction step differs from the stopped position of the needle after the ordinary control due to the backlash of the gear mechanism.